FIG. 1 shows an example of a double clad optical fiber 11. The double clad optical fiber 11 generally includes a waveguide core 10 having a core refractive index 12, an inner waveguide cladding 14 around the core having an inner cladding refractive index 16, and an outer waveguide cladding 18 around the inner cladding 14 and having an outer cladding refractive index 20, and a jacket 22 around the outer waveguide cladding 18, having a jacket refractive index 24, typically higher than the outer cladding refractive index 20.
In the delivery of high power optical signals and in the making of high power fiber lasers and amplifiers, the core 10 can be of doped silica, the inner cladding 14 can have one or more layers of silica glass or doped silica glass, and the outer cladding 18 of non silica material can have an significantly lower refractive index 20 that prevents light from escaping the core 10 and the inner cladding 14. The outer cladding 18 can be made of a low index polymer such as silicone, fluorinated ethylenic-cyclo oxyaliphatic substituted ethylenic copolymer, or another material, but it is common to use fluoroacrylate optical fibers which are characterized by the fact that the material of the second waveguide cladding 18 is a fluoroacrylate, such as product number PC363, PC373, PC375, or PC409 manufactured by SSCP CO. or product DeSolite® DF0007 manufactured by DSM Desotech. In certain cases, the core 10 and the inner cladding 14 are of the same material and therefore can have the same refractive index. To provide a complete example, the protective jacket can be made of a high index acrylate, for instance such as DSM Desotech's product number DS-2015, product number 3471-2-136 or SSCP CO.'s product number UVF-HTS-001. The main function of the jacket is to improve the mechanical performance of the fiber.